1. Field of the Invention
The present invention relates generally to the field of solid part fabrication. More particularly, the present invention relates to the fabrication of parts by directed droplet deposition (D.sup.3). Specifically, a preferred implementation of the present invention relates to deposition of fully dense, close tolerance parts with a deflected droplet stream that is steered. The present invention thus relates to a fabrication technique of the type that can be termed directed droplet deposition (D.sup.3).
2. Discussion of the Related Art
Forming precisely shaped, high strength parts is a major part of the world economy. Fields as diverse as automobiles, medicine, electronics, and national defense are critically dependent on precisely shaped parts. What is urgently needed is a manufacturing technique that can reduce the number of steps involved in going from engineering drawing to the final part.
As is known to those of skill in the art, a previously recognized impediment to rapid manufacturing is the fabrication of hard tooling for component manufacture. Presently, the majority of tooling used for metal forming, plastic injection, die casting, and investment casting is machined from large blocks of metal..sup.(1) This traditional manufacturing approach involves high costs and long lead times. In addition, the associated traditional manufacturing techniques also pose environmental risks through the generation of significant waste metal and machining fluid.
Another previously recognized impediment to rapid manufacturing is the production of prototypes for verification of design. Presently, prototypes are manufactured in the same way that the tooling produced or by alternate techniques involving less robust or costly tooling. In most cases, the prototypes manufactured in this manner have properties and performance characteristics that are inferior to the desired part. Again, this traditional approach is costly, requires long lead time and poses environmental risks.
Therefore, what is needed is a new approach that can be used to produce tooling and/or prototypes quickly and with less environmental risk. Heretofore, these requirements have not been fully met.
One unsatisfactory previously recognized approach, in an attempt to solve the problems referred to above, involves the use of computer-aided-design (CAD) and numerical control (NC) machining. This involves the use of software to generate instructions for computer controlled machines directly from CAD or electronic representations of parts. The instructions, called NC tool paths, are used to drive NC machine tools to automatically machine parts from blocks of metal. However, the generation of NC tool paths can be complicated, time-consuming, and involve excessive trial and error, especially for parts of complex shape. Also, the process still generates a significant amount of waste metal and machining fluid.
Another more recent, but still somewhat unsatisfactory approach for the production of parts and prototypes is the use of rapid prototyping (RP) technologies. Starting from CAD descriptions of solid or surface models of a part, RP technologies allow the production of three-dimensional (3D) physical models by the assembly of sequential layers of material corresponding to successive cross-sections of the part. These sequential cross-sections collectively define the shape of the object. Initially, RP technologies such as stereolithography (SLA), selective laser sintering (SLS), and laminated object manufacturing (LOM) produced resin, polymer, or laminated paper parts. More recently, they have evolved to the use of polymer coated metal powders and the use of lasers to fuse successive cross-sections of metal powders for the production of metal parts or prototypes (SLS, Three-Dimensional Printing, Laser Engineered Net Shaping process, Directed Light Deposition, Shape Deposition Manufacturing, etc.). However, all these processes use precision powder feedstock and have low deposition rates, making them expensive and slow, and typically produce porous parts that must be subsequently densified or infiltrated by a secondary metal to close porosity, making them unsuitable as the final part.
Meanwhile, in other fields of endeavor, those of skill in the art have been forming charged droplets and directing these charged droplets with electrostatic fields..sup.(2-3) The below-referenced U.S. Patents disclose methods of forming charged small droplets that were satisfactory for the purposes for which they were intended. The entire contents of U.S. Pat. Nos. 5,431,315; 5,407,136; 5,266,098; 5,062,936; and 4,264,641 are hereby expressly incorporated by reference into the present application.
Within this application several publications are referenced by superscripts composed of Arabic numerals within parentheses. Full citations for these, and other, publications may be found at the end of the specification immediately preceding the claims. The disclosures of all these publications in their entireties are hereby expressly incorporated by reference into the present application for the purposes of indicating the background of the present invention and. illustrating the state of the art.